A sash window requires considerable effort in an opening and closing operation due to the weight of window and may sometimes move down from the state at rest by its own weight. To prevent such situation, for example, U.S. Pat. No. 2,477,069 describes a spiral balance device in which a balanced load is generated corresponding to the weight of the window when the window is opened and closed to maintain balance with the weight of the window. This spiral balance device has a spiral rod and a torsion spring within a pipe. When the window is moved downwardly, the spiral rod moves downwardly within the pipe together with the window and winds a torsion spring, and the restoring force of the wound torsion spring functions to pull up the spiral rod and maintain balance with the weight of the window. In more detail, the spiral balance device has a pipe; an anchor provided within the upper end of the pipe; a coupling which is journaled at the lower end of the pipe and has, at its center, a slot through which a spiral rod is inserted; a torsion spring is housed within the pipe, the upper end of which is fixed to the anchor and the lower end of which is fixed to the coupling; and a spiral rod inserted through the interior of the torsion spring and having a screw section which is formed in a longitudinal direction and the lower end of the spiral rod projecting downwardly out of the pipe. Generally, such spiral balance devices are produced by balance manufacturers and delivered to window manufacturers in such a state that the torsion spring is not wound, namely, no tension is applied to the torsion spring.
The window manufacturers fit the spiral balance device received from the balance manufacturers into a window frame, fix the upper end of the pipe to the window frame, and then directly connect the lower end of the spiral rod downwardly projecting from the lower end of the pipe to a connecting member fixed to the window, to fabricate a sash window. Or, the window manufacturers may connect the lower end of the spiral rod to a slide block slidably fitted to a window frame and connect the spiral rod to a connecting member of the window via the slide block, to fabricate the sash window. During this fabrication operation, the window manufacturers are required to preliminarily wind the torsion spring so that the torsion spring has a spring tension corresponding to the window weight to maintain the window at the elevated and opened position. For this purpose, it is necessary to grip and rotate the spiral rod projecting from the lower end of the pipe. In this operation, since the pipe is fixed to the window frame and the operation site is narrow, a special tool is necessarily used, and it is difficult to securely grip the lower end of the spiral rod and appropriately rotate it.
Further, since the restoring force of the wound torsion spring always functions to rotate the spiral rod in a reverse direction, it is not easy to further rotate the spiral rod against the restoring force. In addition, when the spring is wound, the spring tension varies by the function of spring-back and is therefore unstable immediately after winding the spring. If the spring is set in the window under such condition that the spring tension is not yet stabilized, the expected spring tension cannot be generated, and it is likely that the window cannot be held securely. For this reason, the spiral balance device is usually left to stand for a few days until the spring tension is stabilized with the lapse of enough time, and thereafter correctly adjusted. Otherwise, the fabricated window cannot be shipped. Accordingly, for conventional spiral balance devices, it takes a long time to complete final fabrication.
The spiral balance device described in the above US patent is constituted in such a way that the spring torsion can be adjusted after fabrication, but when the spring is incorporated into the window the first time, it is required to preliminarily wind the torsion spring. The adjusting device described in the above US patent is constituted in such a way that one end of the torsion spring is fixed to a notched rotation tube, and a pin is inserted into the rotation tube to make it possible to rotate the tube and wind the spring. To enable the rotation tube to turn, it is necessary to dispose a hole provided in the rotation tube, a pin to be inserted into the hole, and an opening section disposed on a fixed tube through which the pin is inserted into a pipe. To dispose these constituting parts, operation steps are required to cut away a part of the rotation tube, pipe, fixed tube and the like to form a hole or an opening. Accordingly, the conventional balance adjustment device has a complicated structure and its production is cumbersome.
US Patent Publication No. 2008/235905 describes a spiral balance device which can be delivered from balance manufactures to window manufacturers in such a state that tension is preliminarily applied to a torsion spring. In the spiral balance device described in this publication, a spiral rod is urged by a torsion spring so that the spiral rod can be pulled toward the upper end of a pipe. Into an anchor disposed at the upper end of the pipe, a pre-tensioning insert is installed with which the upper end of the spiral rod is engaged. By this structure, rotation of the spiral rod is usually stopped by the pre-tensioning insert. When the torsion spring is further wound, the spiral rod is pulled toward the lower portion of the pipe to disengage the upper end of the spiral rod from the pre-tensioning insert. By this operation, the spiral rod is placed into a state that it can rotate relative to the pre-tensioning insert. Then, the spiral rod is rotated to wind the torsion spring.
In the spiral balance device described in the above US publication, when the torsion spring is further wound, a force tending to rotate the spiral rod in a reverse direction is exerted on the spiral rod by the restoring force of the preliminarily wound torsion spring. Therefore, to further wind the torsion spring, it is required to firmly hold the lower end of the spiral rod and turn it so as to overcome the restoring force tending to rotate the spiral rod in a reverse direction. Such an operation needs powerful force and is cumbersome. As mentioned above, to rotate the spiral rod, it is necessary to withdraw the spiral rod a predetermined length out of the lower end of the pipe and maintain such a state that the pre-tensioning insert and the upper end of the spiral rod are disengaged. However, when the torsion spring is further wound, a strong force to pull the spiral rod toward the inside of the pipe is gradually exerted. For this reason, the spiral rod is pulled up and easily engaged with the pre-tensioning insert, whereby it becomes further difficult to rotate the spiral rod in such a state that it is withdrawn out of the pipe and stays at the predetermined position.
As mentioned above, when the torsion spring is further wound, it is required to withdraw the spiral rod against the pulling force exerted by the torsion spring and to insert the spiral rod and make the upper end thereof engage with the pre-tensioning insert at the upper position of the pipe against the restoring force tending to rotate the spiral rod in a reverse direction. As explained above, in the spiral balance device described in the above US publication, it is necessary to conduct an operation of withdrawing the spiral rod in an axial direction and elevate it. In addition, it is difficult from the outside of the pipe to grasp the extent of winding, i.e., how much the spring has been wound, and therefore the state of adjustment cannot be clearly confirmed.